Detection of pathogenic Leptospira from field-collected water samples as an indicator of predicting leptospirosis outbreak

Abstract

Leptospirosis is a zoonotic infectious disease caused by the pathogenic Leptospira with an estimated pooled case fatality ratio of 7% in Sri Lanka. Humans acquire leptospirosis through direct contact with the urine of infected reservoir mammals or, most frequently, through contaminated water. Rainfall and floods have been associated with regular leptospirosis outbreaks in the country. Hence this study aimed to isolate pathogenic Leptospira from environmental water samples as a predictor of outbreak, to commence prophylaxis antibiotics for risk groups. A prospective study was performed to detect pathogenic Leptospira in water samples collected from geographical localities, where laboratory confirmed leptospirosis patients reside (index cases=87). The control water samples were collected from areas in which patients with acute febrile illnesses but not leptospirosis reside (control cases=87) for comparison. A cluster with index/control case site and neighborhood situated within 200m radius was selected. Water samples (50mL) were collected from each site into sterile polypropylene centrifuge tubes and centrifuged at 3,000 g for 30 minutes at room temperature. DNA from the pellet was extracted using the QIAamp Viral RNA Mini Kit (QIAGEN GmbH, Hilden, Germany) and tested by a previously validated real time PCR designed to detect pathogenic Leptospira. Results showed 34% (23/67) and 5.8% (4/68) water samples from index and control clusters were positive for pathogenic Leptospira respectively. Statistically significant positivity was noted between index and control clusters (χ2=17.1, p<0.00). The result of the study shows a high likely hood of human acquiring the infection through occupational, recreational and or avocational activities done in water sources in close environments. Hence, the study indicates the possibility of using water testing as an indicator for early detection of leptospirosis outbreaks as well as for the identification of possible geographical expansions.